We studied the effects of lymphocytapheresis in five patients with chronic progressive MS. Ten lymphocytapheresis treatments were given in 2 weeks, followed by 1 treatment every 2 weeks for 2 to 6 months. Four of five patients had a fall in the circulating lymphocyte count during the initial treatment, and in three patients a modest lymphopenia was sustained with maintenance therapy. In patients with abnormal T4:T8 ratios, no improvement in the T4:T8 ratio occurred. There was no apparent clinical effect in this pilot study.